Deinking a cellulosic substrate using magnesium hydroxide

ABSTRACT

A composition and method for deinking is disclosed. The composition and method contain an activated magnesium hydroxide or a magnesium hydroxide.

FIELD OF THE INVENTION

The invention pertains to compositions and methods for deinking acellulosic substrate.

BACKGROUND OF THE INVENTION

Efficiently removing ink from secondary fiber without impacting fiberquality is one of the major challenges in paper recycling. Currently,the most widespread method of removing ink from secondary fiber is analkaline process that uses sodium hydroxide, sodium silicate, hydrogenperoxide, surfactants and chelants. The caustic is used to elevate thepH in the repulper causing the fiber to swell, which assists in inkdetachment, but also yellows the fiber due to interaction with lignin inmechanical grades, resulting in a brightness loss. Peroxide is added toreduce fiber yellowing, and chelant is added to prevent peroxidedegradation by metals. Surfactants are used to manage the detached inkand prevent redeposition onto the fiber.

While the conventional method of deinking is effective for ink removal,it has disadvantages. When the cost of the chemicals needed to overcomethe unwanted effects of caustic is considered, the alkaline method isquite expensive. Aside from the high cost of the chemicals used,handling caustic can be hazardous, and it is critical to maintain theproper balance of caustic, peroxide and silicate to produce fiber withthe desired optical properties. Moreover, any residual fiber yellowing,or chromophoric generation, that is caused by caustic and cannot beremoved with bleaching is balanced blue dye to the fiber. While this iseffective for achieving a neutral color balance, it reduces ISObrightness, making it difficult to reach brightness targets. Inaddition, a recent study showed that fiber strength and tensile indexwas reduced for secondary fiber deinked under alkaline conditions.Finally, the elevated pH in the pulper saponifies adhesives, therebyintroducing more stickies into the papermaking system, which causerunnability problems for the paper machine.

An improved methodology is therefore desired.

SUMMARY OF THE INVENTION

The present invention provides for a composition comprising: (a)activated magnesium hydroxide; (b) optionally a suspending agent forsaid activated magnesium hydroxide; (c) water; (d) optionally anemulsifier; (e) optionally excluding caustic soda; and (f) optionallyexcluding hydrogen peroxide.

The present invention also provides for a composition comprising: (a)magnesium hydroxide; (b) a suspending agent for said magnesiumhydroxide; (c) water; (d) optionally an emulsifier; (e) optionallyexcluding caustic soda; and (f) optionally excluding hydrogen peroxide.

The present invention also provides for a method of removing ink from acellulosic containing substance comprising: (a) adding to the substancea composition comprising: (1) activated magnesium hydroxide, (2) water,(3) optionally a suspending agent for said activated magnesiumhydroxide, and (4) optionally an emulsifier; (b) optionally excludingadding caustic soda to the cellulosic containing substance; and (c)optionally excluding adding hydrogen peroxide to the cellulosiccontaining substance.

The present invention further provides for a method of removing ink froma cellulosic containing substance comprising: (a) adding to thesubstance a composition comprising: (1) magnesium hydroxide, (2) asuspending agent for said magnesium hydroxide, (3) water, and (4)optionally an emulsifier; (b) optionally excluding adding caustic sodato the cellulosic containing substance; and (c) optionally excludingadding hydrogen peroxide to the cellulosic containing substance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows residual ink data after the application of an activatedmagnesium hydroxide and emulsified TOFA formulation to fiber.

FIG. 2 shows ISO brightness after the application of an activatedmagnesium hydroxide and emulsified TOFA formulation to fiber.

FIG. 3 shows sheet yellowness after the application of an activatedmagnesium hydroxide and emulsified TOFA formulation to fiber.

FIG. 4 shows fiber whiteness after the application of an activatedmagnesium hydroxide and emulsified TOFA formulation to fiber.

DETAILED DESCRIPTION OF THE INVENTION A. Definitions

“Suspending agent” means one or more agents that prevents precipitationof a stabilized dispersion of colloidal particles in solution.

“Activated magnesium hydroxide” means a formulation that includesmagnesium hydroxide plus one or more components that provides additionaldeinking performance over the magnesium hydroxide alone, e.g. oil addedas formulation with magnesium hydroxide. For example, if the magnesiumhydroxide is mixed with an oil and that oil meets the requirements ofproviding additional deinking performance, then the magnesium hydroxideis an activated magnesium hydroxide.

“Recycling process” means any process that involves the handling ofsecondary fibers.

“TOFA” means tall oil fatty acid.

“%” means percent by weight of the composition.

B. Compositions

As stated above, the present invention provides for a compositioncomprising: (a) activated magnesium hydroxide; (b) optionally asuspending agent for said activated magnesium hydroxide; (c) water; (d)optionally an emulsifier; (e) optionally excluding adding caustic soda;and (f) optionally excluding hydrogen peroxide. The present inventionalso provides for a composition comprising: (a) magnesium hydroxide; (b)a suspending agent for said magnesium hydroxide; (c) water; (d)optionally an emulsifier; (e) optionally excluding caustic soda; and (f)optionally excluding hydrogen peroxide.

In one embodiment, the suspending agent is a thickening agent.

In another embodiment, the thickening agent is selected from the groupconsisting of: galactomannans; guar gum; locust bean gum; xanthan gum;para gum; cellulosics; hydroxypropyl methylcellulose; hydroxypropylcellulose; carrageean; alginates; sodium alginates; potassium alginates;ammonium salt alginates; and a combination thereof.

In another embodiment, the composition contains from about 5% to about70% of said activated magnesium hydroxide/magnesium hydroxide, basedupon weight of the composition.

In another embodiment, the composition contains about 47% of saidactivated magnesium hydroxide/magnesium hydroxide, based upon weight ofthe composition.

In another embodiment, the composition contains from about 0.05% toabout 20% of said suspending agent, based upon weight of thecomposition.

In another embodiment, the composition contains about 0.4% of saidsuspending agent, based upon weight of the composition.

In another embodiment, the composition comprises an oil.

In another embodiment, the composition contains from about 2% to about55% of said oil based upon the weight of the composition.

In another embodiment, the composition contains about 30% of said oilbased upon the weight of the composition.

In another embodiment, the oil contains a fatty acid.

In another embodiment, the oil is used to form an oil and wateremulsion.

In another embodiment, the composition contains from about 0.5% to about20% of said emulsifier.

In another embodiment, the composition contains about 3% of saidemulsifier.

In another embodiment, the emulsifier is a surfactant.

In another embodiment, the fatty acid contains a tall oil fatty acid.

In another embodiment, the emulsifier is selected from the groupconsisting of: sorbitol derivatives; polysorbate 80; sorbitanmonolaurate; polysorbate 20; ethoxylated alcohols; sodium laurethsulfate; polyethylene glycol; sulfate esters; sodium lauryl sulfate; anda combination thereof.

In another embodiment, the composition comprises: (a) activatedmagnesium hydroxide/magnesium hydroxide; (b) xanthan gum; (c) tall oilfatty acid; (d) sodium lauryl sulfate; and (e) water.

In a further embodiment the composition is comprised of about 47% ofsaid activated magnesium hydroxide/magnesium hydroxide; about 0.395%xanthan gum; about 30% tall oil fatty acid; and about 3% sodium laurylsulfate.

In another embodiment, the composition excludes caustic soda, optionallycomprising rosin wherein the content of rosin in the composition is fromgreater than 0% to about 30% based upon weight of the fatty acid.

These compositions may be applied in methods of removing ink from acellulosic containing substance/substrate. In the next section, variousembodiments of these applications are discussed.

C. Methods

As stated above, the present invention provides for a method of removingink from a cellulosic containing substance comprising: (a) adding to thesubstance a composition comprising. (1) activated magnesium hydroxide,(2) water, (3) optionally a suspending agent for said activatedmagnesium hydroxide, and (4) optionally an emulsifier; (b) optionallyexcluding adding caustic soda to the cellulosic containing substance;and (c) optionally excluding adding hydrogen peroxide to the cellulosiccontaining substance. The present invention also provides for a methodof removing ink from a cellulosic containing substance comprising: (a)adding to the substance a composition comprising: (1) magnesiumhydroxide, (2) a suspending agent for said magnesium hydroxide, (3)water, and (4) optionally an emulsifier; (b) optionally excluding addingcaustic soda to the cellulosic containing substance; and (c) optionallyexcluding adding hydrogen peroxide to the cellulosic containingsubstance.

The performance of a deinking process can be measured in a variety ofways. Typically, optical properties such as brightness (B), whiteness(L), red/green color balance (a) and yellow/blue color balance (b*) aremeasured on a sheet formed from the resulting deinked fiber. In additionto optical properties, an ink speck count measurement is used toevaluate the efficiency with which the ink is removed. Residual ink canbe expressed in terms of specks/unit area, percent coverage of inkspecks on an area, or effective residual ink concentration (ERIC), whichis commonly expressed in ppm.

In one embodiment, the cellulosic substance is located anywhere in arecycling process up through one or more Rotation accepts.

In another embodiment, the emulsifier is added separately to thecellulosic containing substance.

In another embodiment, the suspending agent is a thickening agent.

In another embodiment, the thickening agent is selected from the groupconsisting of: galactomannans; guar gum; locust bean gum; xanthan gum;para gum; cellulosics; hydroxypropyl methylcellulose; hydroxypropylcellulose; carrageean; alginates; sodium alginates; potassium alginates;ammonium salt alginates; and a combination thereof.

In another embodiment, the composition contains from about 5% to about70% of said activated magnesium hydroxide/magnesium hydroxide, basedupon weight of the composition.

In another embodiment, the composition contains about 47% of saidactivated magnesium hydroxide/magnesium hydroxide, based upon weight ofthe composition.

In another embodiment, the composition contains from 0.05% to about 20%of said suspending agent, based upon weight of the composition.

In another embodiment, the composition contains about 0.4% of saidsuspending agent, based upon weight of the composition.

In another embodiment, the composition further comprises: an oil.

In another embodiment, the composition contains from about 2% to about55% of said oil based upon the weight of the composition.

In another embodiment, the composition contains about 30% of said oilbased upon the weight of the composition.

In another embodiment, the composition contains from about 0.5% to about20% of said emulsifier.

In another embodiment, the composition contains about 3% of saidemulsifier.

In another embodiment, the oil contains a fatty acid.

In another embodiment, the oil is used to form an oil and wateremulsion.

In another embodiment, the emulsifier is a surfactant.

In another embodiment, the fatty acid contains a tall oil fatty acid.

In another embodiment, the emulsifier is selected from the groupconsisting of: sorbitol derivatives; polysorbate 80; sorbitanmonolaurate; polysorbate 20; ethoxylated alcohols; sodium laurethsulfate; polyethylene glycol; sulfate esters; sodium lauryl sulfate; anda combination thereof.

In another embodiment, the composition excludes caustic soda.

In another embodiment, the composition further comprises rosin,optionally wherein the content of rosin in the composition is fromgreater than 0% to about 30% based upon weight of the fatty acid.

In another embodiment, the method of removing ink from a cellulosiccontaining substance comprises: (a) adding to the substance acomposition comprising: (1) activated magnesium hydroxide/magnesiumhydroxide, (2) xanthan gum, (3) tall oil fatty acid, (4) sodium laurylsulfate, and (5) water; (b) optionally excluding the addition of causticsoda to the cellulosic containing substance; and (c) optionallyexcluding the addition of hydrogen peroxide to the cellulosic containingsubstance.

In a further embodiment, the composition is comprised of about 47% ofsaid activated magnesium hydroxide/magnesium hydroxide; about 0.395%xanthan gum; about 30% tall oil fatty acid; and about 3% sodium laurylsulfate.

The methodologies of the present invention can be applied to a paperrecycling process, when deinking is desired.

In one embodiment, the composition is added to a paper recycling processin at least one of the following locations: a pulper; dilution stage;flotation cell thickening stage; and a kneader.

In another embodiment, the composition is added in a pulper of a paperrecycling process.

In another embodiment, the composition is added at a dilution stage of apaper recycling process.

In another embodiment, the composition is added at a thickening stage ofa paper recycling process.

In another embodiment, the composition is added in a flotation cell of apaper recycling process.

In another embodiment, the composition is added in a kneader of a paperrecycling process.

In another embodiment, the substance contains one or more paper fibers.

In another embodiment, the paper fibers are secondary fibers in a paperrecycling process.

The following examples are not meant to be limiting.

EXAMPLES

A formulation for the removal of ink from secondary fiber using underreduced alkalinity conditions can best be realized by thickening asample of deionized (“DI”) water with xanthan gum at 2.0% by weight withgentle stirring. Adding a 50/50 mixture of polysorbate 80 andpolysorbate 20 at 2.5% by weight for the combined surfactant to thexanthan gum enables the emulsification of tall oil fatty acid at 5.15%by weight with mixing of the solution. While mixing, magnesium hydroxideparticles with 1 micron particle size were added to the emulsion at aconcentration of 5.15% by weight. To achieve a stable formulation whilemaintaining a fluid viscosity capable of being pumped, the overallsolids in the formulation were in the range of 15%, but can be increasedto higher solids percentages.

For example, 0.4 g of xanthan gum was added to 20 ml of DI water withgentle stirring to assist in dissolving the powder. 0.25 g ofpolysorbate 20 and 0.25 g of polysorbate 80 were added to the xanthangum solution. 1.2 g of TOFA was added and emulsified with gentlestirring, along with 1.2 g of magnesium hydroxide, resulting in a stableemulsified slurry of activated magnesium hydroxide and TOFA. Theprepared sample was suitable to remove ink from 120 g of secondaryfiber.

The deinking treatment can then be added to secondary fiber in therepulping process at a high consistency of fiber and an elevatedtemperature (˜35-60° C.) where the sheets were disintegrated into fiber.To assist in producing a sheet with higher brightness, peroxide wasadded to the pulper upon the addition of the disclosed formulation.Traditionally, hydrogen peroxide was added to the pulper in causticdeinking at a ratio of 0.6:1 caustic to hydrogen peroxide. Given thatwhen replacing caustic (sodium hydroxide) with magnesium hydroxide, thereplacement ratio is 1.0:0.73 NaOH:Mg(OH)₂, hydrogen peroxide was addedat a ratio of 2.28:1.0 hydrogen peroxide to activated magnesiumhydroxide.

Upon complete repulping, the disintegrated secondary fiber was dilutedand placed into a floation cell where detached ink was separated fromthe fiber using an agitator and air bubbles passing from the bottom tothe top of the cell, collecting dislodged ink particles. This creates afroth that carries the ink and was removed from the top of thefloatation cell. Typical floatation temperatures range from 35-60° C.Upon completion of the floatation stage, the deinked fiber was collectedand residual ink and optical measurements are made.

Measurement Methods:

For this study, optical properties of deinked fiber were measured usinga Technidyne Colortouch 2 on handsheets prepared according to TAPPImethod T218. In the interest of reducing effects of sample preparation,ink speck counts were performed using a PAPRICAN Ink Scanner by Op-Teston the same sheets used for optical characterization.

Sample Results:

As shown in FIG. 1, the residual ink remaining after the deinkingprocess was measured on handsheets made from deinked fiber. The efficacyof the activated magnesium hydroxide and emulsified TOFA formulation isclear when compared to the variations on the formulation and theconventional caustic deinking benchmark.

As shown in FIG. 2, the ISO brightness was measured on handsheets madefrom deinked fiber. The data shows that the disclosed deinkingformulation is capable of outperforming the conventional causticdeinking treatment in brightness gain.

As shown in FIG. 3, the sheet yellowness, as measured on handsheetsprepared from deinked fiber, is slightly higher for the disclosedformulation, but is not too high to overshadow the benefits of theformulation has for ink removal and the other optical properties.

As shown in FIG. 4, the fiber whiteness was measured on fiber deinkedwith the experimental formulations. Similar to the trend observed in thebrightness measurements, the proposed invention outperforms theconventional caustic deinking treatment.

We claim:
 1. A method of removing ink from a cellulosic containingsubstance comprising: (a) adding to the substance a compositioncomprising: (1) magnesium hydroxide, (2) xanthan gum, (3) tall oil fattyacid, (4) sodium lauryl sulfate, and (5) water; (b) optionally excludingthe addition of caustic soda to the cellulosic containing substance; and(c) optionally excluding the addition of hydrogen peroxide to thecellulosic containing substance.
 2. The method of claim 1 wherein thecomposition is comprised of about 47% of said magnesium hydroxide; about0.395% xanthan gum; about 30% tall oil fatty acid; and about 3% sodiumlauryl sulfate.